Ignition means for radial engines



y 1942- K. A. HARMON IGNITION MEANS FOR RADIAL- ENGINES Filed April 18,1939 2 Sheets-Sheet} I QINVENTOR Aim/(WA. Mam/01v +W TTORN Ys May 12,1942; K. HARMQN IGNITION MEANS FOR RADIAL ENGINES Filed April 18, 1939ZSheets-Sheet 2 ?atented may l2, 1942 UNITED STATES PATENT OFFICEIGNITION MEAN S FOR RADIAL ENGINES Kenneth A. Harmon, Longmeadow, Mass,assignor to Wico Electric Company, West Springfield, Mass., acorporation of Massachusetts Application April 18, 1939, Serial No.268,559

3 Claims.

cam. The reason for this arrangement is that the lobes of the cam areirregularly spaced in order to secure ignition accurately when thepistons are in firing position. Due to the use of a master connectingrod for one cylinder of each series of radial cylinders and thearticulation of the other connecting rods of the same series to themaster connecting rod instead of directly to the crankshaft, the pistonsdo not reach firing position in their respective cylinders at equalangular movements of the crankshaft. equally spaced lobes of theignition cam compensate for the aforesaid discrepancy and cause ignitionto occur accurately when the pistons are in firing position.

Many difficulties attend; the use of an ignition cam of this class in anengine having a large number of cylinders, such as eighteen for example. The cam must be made large in diameter to accommodate so manylobes and it has to be made by special methods which are expensive.

Then, in use there is more rapid wear of the breaker points due to therapidity-with whichthey are moved into and out of engagement. It isdesirable to divide the work between two or more breaker arms and, whilethis might easily be done in other types of engines, it has not beenconsidered feasible in engines of the type aforesaid.

This invention has for-its object the provision of a breaker pointmechanism for use in a twin row, four cycle internal combustion engineof the radial cylinder type, characterized by a single cam and twocooperating breaker arms which operate alternately and are so located asto engage the cam at angularly spaced points thereon-the spacing beingsuch that accurately timed ignition can be had for each cylindernotwithstanding the irregular spacing of the lobes of the cam.

The invention will best be understood as the detailed descriptionproceeds and the scope'of the invention will be pointed out in theappended claims.

The un- The invention will be disclosed with reference to theaccompanying drawings, in which:

Fig. '1 is a diagrammatical view of a twin row, radial type of aircraftengine for which the in-' vention is suitable;

Fig. 2 is a fragmentary view taken like Fig. 1 but showing the parts indiiferent'relative posiions;

Fig. 3 is an enlarged view of a breaker point mechanism embodying theinvention;

Fig. 4 is an enlarged view of the'cam for actuating the breaker pointmechanism; and

Fig. 5 is a diagram illustrative of a conventional form of ignitionmeans of which said mechanism forms a controlling part. i

Referring to Fig. 1, there is shown in diagrammatical form a four cycle,eighteen cylinder internal combustion engine, adapted for aircraft. Theengine'is of the radial type with the cylinders arranged in two rows ofnine cylinders each, the cylinders of each row being disposed radiallywith respect to the crankshaft. The nine cylinders of one row areequidistantly spaced in -a circular series and are designated I, 3, 5,1,9, H, l3, l5, and H. The'nine cylinders of the other row are likewiseequidistantly spaced in a circular series and are designated 2, 4, 6, 8,I0, l2, ll, I6 and I8. The crankshaft, marked 20, has a double crank 2|and the two crankpins, marked 22 and 23, are disposed in diametricallyopposed relation. The pistons are shown at 25 and their wrist pins at26. The connecting rod 21 for the piston of cylinder I3 is a so-calledmaster rod and is rigidly joined to a spider 28 which is rotatablymounted on crankpin 22. The connecting rod 29 for cylinder 8 of theother series is likewise a master rod and is rigidly fixed to a spider30 which is rotatably mounted on crankpin 23. The other connecting rods3! of the first series are articulated to spider 28.by pins 32 which areequally spaced in a circular series concentric with crankpin 22. Theother connecting rods 33 of the other series are articulated in the sameway to spider 30 by pins 34. The crankshaft 20 is connected by anysuitable means, such as that conventionally indicated at 36, to drive ashaft 35 at half speed.

Shaft 35 rotates in the same direction as shaft 20 and drives thebreaker point -mechanism shown in Fig. 3.

In this diagram it maybe assumed for theengine shown in Fig. 1, andassuming next in firing order, is cylinder 9. and 13 are spaced 80degrees. However, the piston of the cylinder 9 will not be exactly infiring position after an 80 degree movement of crank 22.This'discrepancy results from the connection of the rod 3| to spider 28rather than directly to the crank 22. For example, in Fig. 2, the crank22 has been turned 80 degrees counterclockwise from its Fig. 1 position,but the piston 25 for cylinder 9 has not quite reached top dead centerposition, as evidenced by the fact that the center line of rod 3| doesnot quite coincide with the radial center line 31 of cylinder 9. If onemoves the crank 22 until the piston in cylinder 9 does reach top deadcenter position and measures the angle of crank movement, such anglewill be found in this particular example to be 83 degrees.

Onetmay determine for the entire group of 18 cylinders the angularmovement between successive pairs of cylinders (taken in the'order oftheir firing)- necessarysto bring the pistons into firing position. As aresult, one would obtain a series of 18 angles each approximately 80degrees but varying slightly therefrom. Having this series of angles,one may then lay out correctly the lobes on the cam which actuates thebreaker point mechanism of the ignition means. The angles of theaforesaid series are divided by two to secure a series of anglesrepresenting the angles between successive lobes of the cam.

Due to the irregular spacing of the lobes of the cam, it has beenthought necessary heretofore in order to secure accuracy of firing touse one large cam having as many lobes as there are cylinders (18breaker arm to ride on the cam. Thi means that the cam must berelatively large in diameter to accommodate so many lobes. If the cam isconstructed as a polygon inscribed within a circle (like the cam shownin Fig. 4) the radial distance (such as 3:) between the high and lowpoints of the cam will be very small and too small for the purpose. InFig. 4 the nine lobe cam Cylinders 9 there shown -is drawn twice itsactual size.

Therefore, the distances are actually much less than shown.Consequently, with an 18 lobe cam the distances (corresponding to thedistances a) would be much smaller and so small that it is necessary torecess the cam between the lobes by undercutting below a horizontal linewhich ninevlobe cam in the following manner. Such cam will be suitablefor one row of cylinders of the engine, say those having odd numbers.These cylinders fire in the following orderi3, 9, 5, I, I5, H, I, 3 andi1, and all fire during two revolutions of the crankshaft 20 and therespective angular movements of crankpin 22 necessary to bring thepistons 25 of these cylinders successively into firing position are inthis particular case 83, 19, 74, 835, 81, 835, 74, 79, and 83. Theseangles are halved and the resulting series is used, as shown in Fig. 4,as the spacing between the lobes 40. The arrow 42' represents a breakerarm in position to fire cylinder IS. The cam rotates counterclockwiseand the numerals within the circles on the cam represent the variouscylinders. It now one should work outin a similar way the angularspacing for the lobes of another cam suitable for use with the cylindersin the even numbered row, the second cam will be found to be identicalwith the first. However, ifthe cooperating breaker arm for this secondcam were in the same locationas arrow 42', the cam would have to beangularly oflset from the first in order to function correctly. If,however, the two breaker arms are spaced apart by the amount of thisofiset (the second breaker is indicated by thearrow 43 in Fig. 4) thesecond cam could be turned until its contour exactly coincides with thefirst cam. Therefore; one cam can be used for both breaker armsproviding these arms are correctly spaced, as shown in Fig. 4.

in this case) and to provide one interconnects successive lobes. As apractical matter a cam, such as described, is very expensive tomanufacture because the undercutting has to be done. by grinding withexceedingly close accuracy The present invention is directed to the useof a single cam having half the number of lobes as there are cylindersand to the use of two breaker arms to cooperate with the one cam.Heretofore, such an arrangement has been considered impossible becauseof the described irregularity of firing positions and the compensatoryirregular spacing of the lobes of the cam. However, I have worked out acertain angular spacing of these breaker arms relatively to the cam,which enables both arms to be correctly actuated at properly timedintervals to secure ignition in each cylinder at exactly the time whenits piston reaches firing position.

Taking as a specific illustrative example, the that the firing order ofthe cylinders is l3, 2, 9, l6, 5, I2, I, 8, l5, 4, H, I8, I, I4, 3, ill,I! and 6, I determine the angular spacing of the lobes 40 of a Thespacing in this case is 140 degrees and it is determined by halving theangle of 280 degrees which is the angle through which the crankpin 23 ofthe even-numbered row of cylinders must travel in order to bring thepiston 25 of its "master rod cylinder 8 into firing position after themaster rod cylinder i3 01 the odd-numbered row has fired. Thus, in Fig.1, cylinder I3 is shown in firing position and crankpin 23 must turncounterclockwise through an angle of 280 degrees before the piston incylinder 8 moves into firing position. Since cam shaft 35 makes onerevolution while the crankshaft makes two, the angle is halved todetermine the spacing for the breaker arms.

In Fig. 3 the breaker point mechanism is shown, the breaker arms 42 and43 (located like the arrows 42 and 43' in Fig. 4) have their leading orcam-contacting ends spaced 140 degrees. Each breaker arm is ofinsulating material pivoted at 45 to a plate which is adjustably fixedin the usual way to a stationary support 41. Each arm carries a breakerpoint 48 to cooperate with a fixed breaker point 49 on plate 46. Theright hand breaker point 49 is insulated from plate 46 as indicated. Thearms are urged toward the cam 4| and the breaker points 48 and 49 urgedwhich rotates counterclockwise at half engine speed and successivelyconnects with the contacts shown. These contacts are numbered from I tol8 inclusive and are connected to the spark plugs of the respectivecylinders bearing corresponding 'in the appended claims.

but unprimed numerals. Thus, the contact I3 is connected by a wire 58 tothe spark plug 59 of cylinder l3.

In operation, the breaker arm 42 has just been actuated by cam 4! toopen the circuit to primary coil 55 and the distributor arm 51 is thenenturns cam 4| and arm 51 through an angle of 20 degrees, and in thisposition the primary circuit is broken by actuation of breaker arm 43 ata time when arm 51 connects with contact 2', thereby firing cylinder 2.Continued movement of the engine crankshaft will cause cam 4| to breakthe primary circuit and cause firing of the cylinders in the order shownin Figs. 4 and 5 which is the preestablished firing order first abovedescribed.

To secure a clear understanding of the invention, the factors of oneparticular engine have' been given, such as the number of cylinders,number of rows of cylinders, spacing of the crankshafts, and spacing ofthe so-called master cylinders, and a particular spacing of cam lobeshas been worked out to suit this engine. Obviously, all these factorsmay be varied and, if varied, a difl'erent spacing of cam lobes willresult. Therefore, I do not intend to be limited by the various factorsand dimensions herein stated, except insofar as they maybe included WhatI claim is:

1. In a four-cycle internal combustion engine or the type wherein thecylinders are arranged in a plurality of rows with a plurality ofcylinders in each row and the cylinders in each row radially disposed ina circular series about the axis of the crankshaft, and wherein thecrankshaft has a plurality of cranks and master connecting rods one foreach row, and one piston of one cylinder in each row is connected bysaid master rod to one of said cranks and the piston of the othercylinders in the same row are connected by rods articulated to themaster rod for such row, a single cam driven from the crankshaft at halfits speed and having a circular series of angularly spaced lobes equalin number to the number of cylinders in one said row, and a plurality ofbreaker point mechanisms one for each row. of cylinders, each mechanismcooperating with the one cam but at angularly spaced locationsrelatively thereto, the angle between the cam-contacting parts of twosuccessive mech.

anisms being equal to half the angle which the crank of one row musttravel from its position at the time whenthe master piston of anotherrow is in firing position to its position at the time when the masterpiston of the first-named row is in firing position.

2. ma four-cycle internal combustion engine, wherein the cylinders arearranged in two rows with a plurality of cylinders in each row and thecylinders in each row being radially disposed in a circular series aboutthe axis of a crankshaft, having two cranks one for each said row, andwherein each crank is connected by a master connecting rod to the pistonin one cylinder of its row and the pistons of the other cylinders of thesame row are connected by rods articulated to the master rod of suchrow, a single cam driven at half the speed of the crankshaft and havinga circular series of angularly spaced lobes equal in number to thenumber of cylinders in one row, two sets of breaker points one for'eachrow and each set having a breaker arm to contact the cam and causeopening and closing of the points as the cam rotates, said breaker armshaving their cam-contacting portions angularly spaced by an angle equalto half the angle which the crank for one row must move from itsposition at the time when the master piston of the other row is infiring position, to its position at the time when the master piston ofits row is in firing position. I

3. In a four-cycle internal combustion engine, wherein the cylinders arearranged in two rows with a plurality of cylinders in each row and thecylinders in each row being radially disposed in a circular series aboutthe axis of a crankshaft. having two cranks one for each said row andspaced 180 degrees apart, and wherein each crank is connected by amaster connecting rod to the piston in one cylinder of its row and thepistons of the other cylinders of the same row are connected by rodsarticulated to the master rod of such row, a single cam driven at halfthe speed of the crankshaft and having a circular series of angularlyspaced lobes equal in number to the number of cylinders in one row, twosets of breaker points one for each row and each set havin a breaker armto contact the cam and cause open-

